In vitro activity of human translation initiation factor eIF4B is not affected by phosphomimetic amino acid substitutions S422D and S422E

►Phosphomimetic mutations of S422 have been shown to activate eIF4B in cultured cells. ► We analyzed activity of recombinant eIF4B variants (wt, S422D and S422E)in vitro. ► The mutations do not affect eIF4B activity in 48S complex reconstitution assay. ► S422D and S422E are as active as the wt protein in a cell-free translation system. ► We suggest that S422 phosphorylation may be not sufficient to activate eIF4Bin vitro.